In general, a tractor refers to a vehicle hauling a trailer which is connected to the rear of the vehicle to travel.
A turn signal lamp is mounted on the tractor according to the automobile safety laws, and it is safety signal equipment that helps other vehicles accurately recognizing the tractor having a trailer turning.
When the turn signal lamp is disconnected, in order to notify a failure of the turn signal lamp, the turn signal lamp warns a driver of the disconnection of the turn signal lamp by flickering a signal of an instrument panel of the tractor at a speed of 120 to 250 times per minute, that is more than 85 times per minute in a normal state.
However, even in the case where the trailer is not connected to the rear of the tractor, an electronic control unit (ECU) of the tractor may misjudge the non-connection state of the trailer as the disconnection of the turn signal lamp to notify the failure.
Demand exists for development of a method of accurately notifying a driver of whether a trailer is connected in order to prevent the driver from recognizing a non-connection state of the trailer as a disconnection of a turn signal lamp. Among publicly known technologies in order to provide the aforementioned function in the related art, there is a technology of constructing an air detection switch in an air line, which supplies air to the trailer, and determining whether the trailer is coupled through the air detection switch. A technology of recognizing, by the ECU, whether the trailer is coupled by adding a pull-down resistor and a detection circuit to a trailer lamp channel circuit is available. However, the aforementioned technologies require additional cost for constructing the air detection switch, and the full-down resistor and the detection circuit, thereby increasing the production cost.